1. Field of the Invention
The invention disclosed herein relates to a method and apparatus for removing a liquid in contact with another material from an earth formation and, in particular, to using an electrical submersible pump for the removing.
2. Description of the Related Art
Electrical submersible pumps are generally used by the hydrocarbon production industry to remove a liquid from an earth formation. An electrical submersible pump (ESP) is placed in a borehole that provides access to the liquid. The ESP is electrically energized from a power supply at the surface of the earth. Thus, when energized, the ESP pumps the liquid that has entered the borehole to the surface of the earth for removal.
Other materials may also be present in the borehole. For example, a gas may be present along with the liquid in the borehole. In certain wells, the borehole may have long horizontal lengths to increase flow. It is not uncommon for an ESP to be landed in a section of a horizontal borehole that extends thousands of feet without a casing from the ESP. The geometry of the open-cased borehole is generally not perfectly horizontal allowing for high points in the borehole. The high points in turn can accumulate pockets of the gas.
During pumping operations, the pockets of gas can release all at once causing the ESP to gas lock and stop lifting fluid. Gas locking of the ESP can hamper continued flow of the liquid and water removal thus reducing production. In addition, gas locking can damage the ESP due to mechanical wear from gas affects and/or high temperature from excessive high speed as the gas flows through the ESP.
Another type of material that may be present with the liquid in the borehole is solid matter. Wellbore solids can enter the borehole at a point that is not cased. The solids entrained with the liquid can flow into and out of the ESP causing a potential for future damage. Sometimes the solids in the form of scale can build up on inner surfaces of the ESP or on inner surfaces of the production tubing. If the scale breaks off a surface, the scale may not have sufficient velocity to flow through and out of the tubing. The scale that does not exit the tubing can fall back towards the ESP and onto a check valve if used, plugging the check valve. If a check valve is not used, the scale can fall back into stages of the ESP accelerating mechanical wear, increasing power consumption, and/or plugging the ESP.
Therefore, what are needed are techniques to remove a liquid that is in contact with another type of material from a borehole penetrating the earth without damaging a pump.